I like your idea of a lead platter mat, but as you've found...I don't know how to maintain a constant thickness with sheet lead?
It is so malleable that you can depress it with your fingertip.....
The only solution I can imagine, would be to laminate it between two sheets of glass or acrylic but then you lose the critical benefit of the lead/platter/vinyl interface...👀
Have you listened to the TT-81 before recapping?
Regards

